Perhaps you should try some spelling variations:
quoc quan » qua quan, luc quan, hoc quan
quoc ban » quoc bao, quoc lan, quoc binh
su sach » so sach, vu sach
cua tre » cua te, cuu tre, cua triet
hieu va » lieu va, hieu qua
y nang » ky nang, ly nang, v nang
anh ve » hanh ve, anh va, anh viet
ve cua » le cua, de cua, te cua
va cam » va cham, va cac, va cao
o hoi » co hoi, o hoc, o hai
x hoi » xa hoi, x ho, 5 hoi

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: su sach y nang ((x hoi) or (o hoi)). hieu va cam ((quoc ban) OR (quoc quan)) anh ve cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach y nang ((x hoi) OR (o hoi)). hieu va cam ((quoc ban) OR (quoc quan)) anh ve cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach y nang ((x hoi) or (o hoi)). hieu va cam ((quoc ban) OR (quoc quan)) anh ve cua tre".
• Adding a wildcard symbol may retrieve word variants: su sach y nang ((x hoi) or (o hoi)). hieu va cam ((quoc ban) OR (quoc quan)) anh ve cua tre*.